Traction drive of a rail vehicle for driving and generative braking

ABSTRACT

The invention relates to a traction drive for the driving and generative braking of a rail vehicle or a combination of rail vehicles, a permanent-field synchronous motor and a traction current converter being respectively associated with at least two axles of the rail vehicle or combination of rail vehicles. The traction current converter includes at least one pulse current converter on the engine side, and the clamps of the permanent-field synchronous motor are connected to a change-over switch such that the permanent-field synchronous motor can be connected to a load circuit containing at least one load element, in order to drive the pulse current converter or for generative braking. According to the invention, the load circuits connected to the permanent-field synchronous motors for generative braking are designed such that the brake characteristic lines of the permanent-field synchronous motors differ in terms of characteristic features such as the position of the maximum of the brake torque according to the rotational speed.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of priority to InternationalApplication No. PCT/EP2007/009258 filed 25 Oct. 2007, which claimspriority to German Patent Application No. 10 2006 051 337.1 filed 31Oct. 2006, the contents of which are incorporated herein by reference intheir entirety.

BACKGROUND

The invention is based on a traction drive for driving, and forperforming regenerative braking of a rail vehicle or a combination ofrail vehicles, wherein at least two axles of the rail vehicle or of thecombination of rail vehicles are respectively assigned a permanentlyexcited synchronous motor and a traction current converter, and thetraction current converter has at least one machine-side pulse currentconverter, and the permanently excited synchronous motor is connected atits terminals to a changeover switch in such a way that the permanentlyexcited synchronous motor can be connected to a load circuit containingat least one load element in order to drive the pulse current converteror to perform regenerative braking.

The objective when equipping rail vehicles is to use ever more effectiveand lightweight drive machines. Presently, inverter-fed asynchronousmachines are used as the standard drive machine. However, these machinesoffer little potential for further development in terms of reducingtheir mass and torque density and, when used in rail vehicles, thesemachines usually require a transmission. For this reason, increasingefforts are currently being made to develop and use permanently excitedsynchronous machines as vehicle drives. By virtue of its high torquedensity, this type of machine permits direct drives to be implementedwhile eliminating the transmission means; this allows the mass of thedrive train to be reduced to a very high degree.

Permanently excited synchronous machines have a number of particularfeatures compared to asynchronous technology owing to their permanentexcitation. Therefore, in the case of a rotating machine, for example,it is possible to achieve a braking effect in addition to theinverter-regulated generator mode using purely passive components. Thebraking effect which is achieved by a permanently excited synchronousmachine by connecting braking resistors is disclosed in DE 101 60 612,which defines the generic type.

When the rotating, permanently excited synchronous machine with brakingresistors is connected into the circuit, a characteristic torque curveor characteristic force curve, also referred to below as a naturalbraking characteristic curve, is obtained as a function of therotational speed of the synchronous motor and, therefore, also of thespeed of the vehicle. The braking characteristic curve has a maximumvalue in its profile when plotted against the rotational speed/speed.

The problem when using the regenerative braking effect of a permanentlyexcited synchronous motor is, therefore, that the natural brakingcharacteristic curve does not have a constant braking torque profilewhen plotted against the rotational speed. This constitutes adisadvantage in the braking behavior compared to the technology with aregulated braking force which is conventionally customary.

SUMMARY

The invention is based on the object of developing a traction drive ofthe above-mentioned type in such a way that the braking behavior can beinfluenced selectively.

The basic idea of the invention is that the load circuits that areconnected to the permanently excited synchronous motors in order toperform regenerative braking are embodied in such a way that the brakecharacteristic curves of the permanently excited synchronous motors aredifferent in terms of characteristic features such as the position ofthe maximum braking torque as a function of the rotational speed.

In other words, despite the design of the motors being identical thebraking characteristic curves of the permanently excited synchronousmotors have braking torques of different magnitude when the rotationalspeed is the same owing to the different load circuits. If, for example,the load circuit of one of the synchronous motors gives rise to amaximum braking torque at low rotational speeds, this can compensate abraking torque which is relatively low in comparison at low rotationalspeeds and is generated by another synchronous motor of the rail vehicleowing to a different load circuit. In an analogous fashion, the othersynchronous motor with a maximum braking torque at relatively highrotational speeds can compensate the braking torque of the synchronousmotor which is then lower.

Two or more permanently excited synchronous motors that are identicalbut are provided with different load circuits can then be combined withone another synchronous motor in such a way that, by superimposing thebraking characteristic curves (which are then different), a brakingtorque profile (which is as balanced or constant as possible whenplotted against the rotational speed) is obtained for a bogie, a railvehicle component, an individual vehicle (such as a wagon) or acombination of rail vehicles. This is achieved by adjusting the passiveload circuits of the individual permanently excited synchronous drives.

The more load circuits of the individual drives are matched to oneanother, the better the degree by which the braking torque profile canbe approximated to a constant braking torque. In the simplest case, asdescribed in the following exemplary embodiment, this can be done byusing different resistance values of the braking resistors. However, anydesired connection of resistors, capacitors and/or inductors such aschoking coils is also conceivable.

Advantageous developments and improvements of the invention specified inthe independent claims are possible by virtue of the measures specifiedin the dependent claims.

At least two axles, each with at least one permanently excitedsynchronous motor, a machine-side traction current converter, achangeover switch and a load circuit may be assigned to a bogie of therail vehicle or of the combination of rail vehicles. An approximatelyconstant braking torque profile can then be obtained for each bogie.

Generally, the load circuits of the permanently excited synchronousmotors assigned to the at least two axles can differ in load elementsand/or in having different connections of their load elements. Aparticularly simple embodiment is obtained if the load circuits of theat least two axles merely have different braking resistors, wherein thebraking resistors of the load circuits are embodied, for example, insuch a way that the maximum braking torque of the braking characteristiccurve of the permanently excited synchronous motor assigned to the oneaxle occurs at a lower rotational speed than the maximum braking torqueof the braking characteristic curve of the permanently excitedsynchronous motor assigned to the other axle.

BRIEF DESCRIPTION OF THE FIGURES

An exemplary embodiment of the invention is illustrated in the figuresand will be described in more detail in the following description. Inthe figures:

FIG. 1 is a schematic illustration of a traction drive for analternating current vehicle according to an embodiment of the invention.

FIG. 2 is a schematic illustration of a bogie having two axles, each ofwhich being equipped with a traction drive in the manner of FIG. 1.

FIG. 3 shows braking characteristic curves of the traction drive of thebogie in FIG. 2.

DETAILED DESCRIPTION

In FIG. 1, a traction drive 1 for an alternating current vehicle, alsoreferred to as an AC rail vehicle, is illustrated wherein, a tractiontransformer is denoted by 2, a traction current converter by 4, apermanently excited synchronous motor by 6 and a brake device by 8. Thetraction transformer 2 has a primary winding 10 and a plurality ofsecondary windings 12 (only two secondary windings 12 of which beingillustrated). The traction current converter 4 has two four-quadrantchoppers 14, an absorption circuit 16, a capacitor battery 18, anovervoltage protection device 20 and a machine-side pulse currentconverter 22. The two four-quadrant choppers 14 are each linked on thealternating voltage side to a secondary winding 12 of the tractiontransformer 2 and are connected electrically in parallel on the directvoltage side. The absorption circuit 16, the capacitor battery 18, theovervoltage protection device 20 and the direct-voltage-side inputconnections of the machine-side pulse current converter 22 are connectedelectrically parallel to the two direct-voltage-side connections 24 and26 of this feed circuit. On the output side, the machine-side pulsecurrent converter 22 can be connected to connections of the permanentlyexcited synchronous motor 6.

The brake device 8 is composed, per phase, of the permanently excitedsynchronous motor 6, a braking resistor 28 and a changeover switch 30.These braking resistors 28 are connected electrically in, for example, astar configuration and each have, for example, a constant resistancevalue. A triangular circuit is alternatively also conceivable. Thechangeover switches 30 are linked in such a way to the outputs of themachine-side pulse current converter 22 and to the inputs of thepermanently excited synchronous motor 6 such that the inputs of thepermanently excited synchronous motor 6 can be connected on one side tothe braking resistor 28 and on the other side to the outputs of themachine-side pulse current converter 22.

These changeover switches 30, which are also referred to as failsafeswitches, can be activated electrically, mechanically or pneumatically.As soon as these changeover switches 30 have moved from the “drive”operating position, i.e., the terminals of the permanently excitedsynchronous motor 6 are connected to the outputs of the machine-sidepulse current converter 22, into the “brake” operating position, i.e.,the terminals of the permanently excited synchronous motor 6 areconnected to the braking resistors 28 which are connected in a star; thepermanently excited synchronous motor 6 also generates a braking torque,which changes in accordance with the profile of the brakingcharacteristic curve as the speed of the rail vehicle is reduced.Neither the machine-side pulse current converter 22 nor any kind ofregulating means is required to generate the braking torque.

Such a traction drive 1 is described in detail in DE 101 60 612,mentioned above. For this reason, no further reference will be made tothe structure of functionality of the traction drive.

At least two axles of the AC rail vehicle are assigned such apermanently excited synchronous motor 6 with traction current converter4 and the further components according to FIG. 1. In this context, thebraking resistors 28 form a load circuit 32, which is assigned to thesynchronous motor 6 and to which it is connected by means of thechangeover switch 30 to perform regenerative braking. In theregenerative braking mode, such a synchronous motor 6 has a brakingcharacteristic curve 36 such as the one illustrated, for example, inFIG. 3 by means of the dashed line.

A braking characteristic curve, as explained herein, is understood to bethe profile of the braking torque M or of the braking force F plottedagainst the rotational speed n of the synchronous motor 6, which isidentical to the axle rotational speed in the present case of directdrive. This axle rotational speed n is proportional to the velocity ofthe AC rail vehicle. As is apparent from FIG. 3, the braking torque Mfirstly increases steeply as the rotational speed n rises from zero,before said braking torque M drops again after a maximum value M_(max)has been reached. A rotational speed n_(Mmax) is assigned to thismaximum braking torque M_(max). The rotational speed n_(Mmax) representsa typical profile of a braking characteristic curve of a permanentlyexcited synchronous motor 6, to which a load circuit 32 with brakingresistors 28 is connected in the regenerative braking mode.

The load circuits 32 of the synchronous motors 6, which are assigned tothe various axles, are embodied in such a way that their brakingcharacteristic curves are different with respect to the rotational speedn_(Mmax) at which the maximum braking torque M_(max) respectivelyoccurs. Two or more permanently excited synchronous motors 6, which areidentical but are provided with different load circuits 32, may becombined with one another in such a way that, by superimposing thebraking characteristic curves that are then different, a braking torqueprofile which is as balanced as possible when plotted against therotational speed n is obtained for a bogie, a rail vehicle component, anindividual vehicle (such as a wagon) or a combination of rail vehicles.This is done by adjusting the passive load circuits 32 of the individualpermanently excited synchronous motors 6. This adjustment is carried outhere by correspondingly selecting and connecting passive load elementssuch as, for example, resistors, choking coils and/or capacitors.

Using braking resistors 28 whose value can be continuously adjusted orswitched simplifies adjustment of the load circuits 32. Within the scopeof the invention, the respective resistance value of the load circuit 32of a permanently excited synchronous motor 6 is adjusted with respect tothe load circuits 32 of the other permanently excited synchronous motors6 before the regenerative brake operates so that it can no longer bechanged during the braking mode.

According to one exemplary embodiment according to FIG. 2, a bogie 34 ofthe AC rail vehicle has two axles, each with at least one permanentlyexcited synchronous motor 6 a, 6 b, one machine-side traction currentconverter 4 a, 4 b, one changeover switch 30 a, 30 b and one loadcircuit 32 a, 32 b. Each of the two drive shafts of the two axles of thebogie 34 are driven by a permanently excited synchronous motor 6 a, 6 b,which synchronous motors 6 a, 6 b are preferably identical, as are alsothe traction current converters 4 a, 4 b. However, the respective loadcircuits 32 a, 32 b may differ. Resistors 28 a with resistance valueswhich are higher than the resistance values of the resistors 28 b of theload circuit 32 b of the other permanently excited synchronous motor 6 bare may be installed in the load circuit 32 a of the one permanentlyexcited synchronous motor 6 a.

The influence of different resistors on the position of the maximumbraking torque M_(max) or the maximum braking force when plotted againstthe rotational speed n within the braking characteristic curve is asfollows. As the braking resistance values decrease, the maximum brakingtorque M_(max) is displaced in the direction of relatively lowrotational speeds n or speeds until the short circuit occurs, i.e., onlythe internal resistance of the drive continues to act. Conversely, asthe braking resistance values increase the maximum braking torqueM_(max) is displaced in the direction of relatively high rotationalspeeds n or speeds. However, the absolute value of the maximum brakingtorque M_(max) of the braking characteristic curve remains the sameprovided that the inductors and capacitors in the brake circuit do notchange.

The one permanently excited synchronous motor 6 a then has the maximumbraking torque M_(max) of its braking characteristic curve 36 (dashedline) at a lower rotational speed n_(Mmax a) than the other permanentlyexcited synchronous motor 6 b whose maximum braking torque M_(max) ofits braking characteristic curve 38 (dotted line) is at a higherrotational speed n_(Mmax b). The maximum braking torque M_(max) is ineach case of equal size since a variation in the resistance valuesdisplaces the maximum braking torque M_(max) but does not change itsmagnitude.

If the braking resistors 28 a, 28 b are connected simultaneously to thecorresponding permanently excited synchronous motors 6 a, 6 b by thechangeover switches 30 a, 30 b, a resulting braking characteristic curve40 is obtained for the bogie 34 by superimposing the brakingcharacteristic curves 36 and 38; this resulting braking characteristiccurve 40 has an approximately constant profile over a large rotationalspeed range starting at low rotational speeds n just above zero, as isapparent from FIG. 3. Alternatively, by superimposing suitable brakingcharacteristic curves, i.e., by means of correspondingly adapted loadcircuits, it would also be possible to obtain a braking torque profilewhich, when plotted against the rotational speed n, increases, decreasesor is predefined in any desired way.

In addition to resistors 28 or instead of them, it is also possible fora load circuit 32 to contain other passive electronic components such ascapacitors and/or inductors, for example, in the form of choking coils.If a resistor 28 and a capacitor are connected in parallel, for example,the maximum braking torque M_(max) is increased. In contrast, by meansof an inductor, which is connected in series with the resistor 28, it ispossible to reduce the maximum braking torque M_(max) of the assigned,permanently excited synchronous motor 6. Generally, a large number ofload circuits 32 are conceivable, either by varying the resistancevalues, capacitance values or inductance values and/or by varying theconnection of the individual components (parallel or serial), thecombination of which brings about desired properties of the superimposedbraking characteristic curve 40, such as, for example an approximatelyconstant braking torque profile when plotted against the rotationalspeed n.

The invention is not restricted to traction drives of vehicles which arefed by an alternating current circuit; rather, the invention can also beapplied in traction drives of vehicles having permanently excitedsynchronous motors, which are fed by a direct current power system, suchas that described, for example, in DE 101 60 612.

1. A traction drive configured to drive and to perform regenerativebraking of a rail vehicle or a combination of rail vehicles, thetraction drive comprising: a permanently excited synchronous motor and atraction current converter each assigned to at least two axles of therail vehicle or of the combination of rail vehicles, wherein thetraction current converter has at least one machine-side pulse currentconverter, and a changeover switch that is connected to the permanentlyexcited synchronous motor that is connected at its terminals in such away that the permanently excited synchronous motor is selectivelyconnected to a load circuit containing at least one load element todrive the pulse current converter or to perform regenerative braking,wherein the load circuits which are connected to the permanently excitedsynchronous motors to perform regenerative braking are configured insuch a way that the brake characteristic curves of the permanentlyexcited synchronous motors are different in terms of characteristicfeatures.
 2. The traction drive of claim 1, wherein the permanentlyexcited synchronous motors which are identical but are provided withdifferent load circuits are combined with one another in such a way thata braking torque profile produced by superimposing the brakingcharacteristic curves increases or decreases when plotted against therotational speed n.
 3. The traction drive of claim 1, wherein the atleast two axles are assigned to a bogie, a rail vehicle component, anindividual vehicle or a combination of rail vehicles.
 4. The tractiondrive of claim 1, wherein the load circuits of the permanently excitedsynchronous motors differ in having load elements which are differentfrom one another and/or in having different connections of their loadelements.
 5. The traction drive of claim 4, wherein the load circuitscontain resistors and/or capacitors and/or inductors.
 6. The tractiondrive of claim 5, wherein the permanently excited synchronous motorsinclude a first and second permanently excited synchronous motor andwherein the load circuits have different braking resistors such that themaximum braking torque M_(max) of the braking characteristic curve of afirst permanently excited synchronous motor assigned to the one axleoccurs at a lower rotational speed n than the maximum braking torqueM_(max) of the braking characteristic curve of the second permanentlyexcited synchronous motor which is assigned to the other axle.
 7. Thetraction drive of claim 1, wherein one of the differing characteristicfeatures is the position of the maximum braking torque M_(max) as afunction of the rotational speed n.